1. Field of the Invention
This invention relates to an image pickup device, a radiation image pickup device and an image processing system. More particularly, the present invention relates to a radiation image pickup device adapted to extend the image pickup area and an image processing system using such a radiation image pickup device. For the purpose of the invention, radiation refers to α rays, β rays, γ rays and so on and includes X-rays.
2. Related Background Art
A film screen system realized by combining intensifying screens and an X-ray film is popularly used for X-ray photography for the purpose of medical diagnosis. With such a system, the X-rays transmitted through an object to be photographed contain information on the inside of the object and are converted into rays of visible light showing intensities proportional to those of the transmitted X-rays by the intensifying screens. Then, the X-ray film is exposed to the rays of visible light.
In recent years, X-ray digital image pickup devices have been marketed. With such X-ray digital image pickup devices, X-rays are converted into rays of visible light with intensities proportional to those of the original X-rays by means of a scintillator and then the obtained rays of visible light are converted into an electric signal by means of a photoelectric converter, which electric signal is then transformed into a digital signal by means of an A/D converter.
More specifically, a known type of X-ray digital image pickup device comprises an ordinary image pickup device formed by arranging elements on a glass substrate, each element having an amorphous semiconductor sandwiched between a pair of electrodes, and a scintillator laid on the image pickup device in order to convert X-rays into rays of visible light. Another known type of X-ray digital image pickup device is realized by two-dimensionally linking modules, each comprising a tapered optical fiber formed by heating and softening a bundle of optical fibers and drawing the softened bundle, a photoelectric converter such as a CCD arranged at the tapered side of the optical fiber and a scintillator laid on the opposite side of the optical fiber.
X-ray digital image pickup devices of the above described types are mostly used for medical diagnosis and other applications. Such a device is required to show a high resolution, a low noise level, an ability of producing moving images and a wide imaging angle so that the doctor may be able to detect the diseased area quickly and make an accurate diagnosis.
However, while X-ray digital image pickup devices comprising amorphous semiconductors typically made of silicon and arranged on a glass substrate are adapted to show a large sensor effective area, they are accompanied by problems including that the size of pixels cannot be reduced because of the manufacturing process and the device characteristics and that the device sensitivity is limited. Therefore, devices of this type are not adapted to high speed operation particularly in terms of displaying moving images.
On the other hand, X-ray digital image pickup devices comprising photoelectric converters such as CCDs realized by using a silicon substrate have a problem that they cannot show a large sensor effective area mainly because of the restrictions in the manufacturing process and the high power consumption level that produces heat, although they are adapted to realize a small pixel size and pick up moving images because they are highly sensitive and can be driven at high speed.
There has been proposed a device comprising an increased number of elements, using optical fibers tapered in such a way that non-sensor areas of the photoelectric converters may not overlap in order to make it show an enlarged sensor effective area. FIG. 1 of the accompanying drawings is a schematic illustration of some of the photoelectric converters of such a device. In FIG. 1, there are shown substrates 1 carrying respective photoelectric converters, scintillators 3 for converting X-rays into rays of visible light showing a wavelength that can be detected by the photoelectric converters, a base member 7, tapered optical fibers 8, protection glass plates 9 and bonding wires 11. Reference numeral 12 in FIG. 1 denotes a ceramic package.
However, a tapered optical fiber is costly and the ratio of dimensional reduction is not stable because the tapering process involves dimensional dispersions. Furthermore, while several tapered optical fibers that are thick and heavy may be linked together, it is not realistic to link a large number of tapered optical fibers in order to produce a sensor effective area necessary for imaging the chest of a subject. Additionally, tapered optical fibers show a poor light transmission factor to a great disadvantage of the device.
FIG. 2 of the accompanying drawings is a schematic illustration of a conventional X-ray moving image system using an image intensifier (I—I). In FIG. 2, reference numeral 16 denotes the I—I. The X-rays striking the light entering surface are converted into electrons, which are multiplied to realize a high sensitivity of the system. The electrons are then converted to rays of light at the light exiting surface to show an image, which is then input to a CCD camera 15.
However, a system comprising such an image intensifier (I—I) inevitably shows large dimensions because it comprises a vacuum tube.
In the case of a CCD image pickup device, peripheral circuits and electrodes are required to be located in areas outside the display pixel area to inevitably make the peripheral marginal area surrounding the effective display area large as shown in FIG. 3A of the accompanying drawings. Additionally, the X-ray image sensor itself faces a limit for downsizing.
X-ray image sensors that are used for dental diagnosis are designed to be put into the mouth of the patient in order to pick up an image of the inside of the mouth. Then, however, it is impossible to take a picture of some of the molar teeth with such an X-ray image sensor. Particularly, it is highly difficult to put such an X-ray image sensor into the mouth of a child and, if such a sensor is forced into the mouth, it can induce a feeling of vomiting on the part of the patient to make the effort for taking a picture abortive.
As described above, it has been highly difficult to realize an X-ray digital image pickup device for medical diagnosis that is adapted to show a moving image with a high resolution if it is made to have a large sensor effective area and show reduced dimensions at low cost.